Package org.apache.velocity.tools.generic

Class RenderTool

  • Direct Known Subclasses:
    ViewRenderTool
    @DefaultKey("render")
public class RenderTool
extends SafeConfig
    This tool exposes methods to evaluate the given strings as VTL (Velocity Template Language) using either a pre-configured context or one you provide directly. 
     Example of eval():
      Input
      -----
      #set( $list = [1,2,3] )
      #set( $object = '$list' )
      #set( $method = 'size()' )
      $render.eval("${object}.$method")

      Output
      ------
      3

 Example of recurse():
      Input
      -----
      #macro( say_hi )hello world!#end
      #set( $foo = '#say_hi()' )
      #set( $bar = '$foo' )
      $render.recurse($bar)

      Output
      ------
      hello world!


 Toolbox configuration:
 <tools>
   <toolbox scope="request">
     <tool class="org.apache.velocity.tools.generic.RenderTool">
       <property name="parseDepth" type="number" value="10"/>
     </tool>
   </toolbox>
 </tools>

    Ok, so these examples are really lame. But, it seems like someone out there is always asking how to do stuff like this and we always tell them to write a tool. Now we can just tell them to use this tool.

    This tool may be used in any scope, however, the context provided for the eval(String) and recurse(String) methods will only be current if the tool is request scoped. If application or session scoped, then the context will be the same one set at the time of the tool's first use. In such a case, each call to eval(String) or recurse(String) will by default create a new Context that wraps the configured one to prevent modifications to the configured Context (concurrent or otherwise). If you wish to risk it and accrete changes then you can relax the thread-safety by setting the 'forceThreadSafe' property to 'false'.

    Of course none of the previous paragraph likely applies if you are not using the core tool management facilities or if you stick to the eval(Context,String) and recurse(Context,String) methods. :)

    This tool by default will catch and log any exceptions thrown during rendering and instead return null in such cases. It also limits recursion, by default, to 20 cycles, to prevent infinite loops. Both settings may be configured to behave otherwise.

    Version:
    $Revision$ $Date$
    Author:
    Nathan Bubna

    • Constructor Detail

      • RenderTool

        public RenderTool()

    • Method Detail

      • configure

        protected void configure​(ValueParser parser)
        Looks for deprecated parse depth and catch.exceptions properties, as well as any 'forceThreadSafe' setting.
        Overrides:
        configure in class SafeConfig

      • setVelocityEngine

        public void setVelocityEngine​(org.apache.velocity.app.VelocityEngine ve)
        Allow user to specify a VelocityEngine to be used in place of the Velocity singleton.

      • setParseDepth

        public void setParseDepth​(int depth)
        Set the maximum number of loops allowed when recursing.
        Since:
        VelocityTools 1.2

      • setVelocityContext

        public void setVelocityContext​(org.apache.velocity.context.Context context)
        Sets the Context to be used by the eval(String) and recurse(String) methods.

      • getParseDepth

        public int getParseDepth()
        Get the maximum number of loops allowed when recursing.
        Since:
        VelocityTools 1.2

      • setCatchExceptions

        public void setCatchExceptions​(boolean catchExceptions)
        Sets whether or not the render() and eval() methods should catch exceptions during their execution or not.
        Since:
        VelocityTools 1.3

      • getCatchExceptions

        public boolean getCatchExceptions()
        Returns true if this render() and eval() methods will catch exceptions thrown during rendering.
        Since:
        VelocityTools 1.3

      • eval

        public String eval​(String vtl)
            throws Exception

        Evaluates a String containing VTL using the context passed to the setVelocityContext(org.apache.velocity.context.Context) method. If this tool is request scoped, then this will be the current context and open to modification by the rendered VTL. If application or session scoped, the context will be a new wrapper around the configured context to protect it from modification. The results of the rendering are returned as a String. By default, null will be returned when this throws an exception. This evaluation is not recursive.

        Parameters:
        vtl - the code to be evaluated
        Returns:
        the evaluated code as a String
        Throws:
        Exception

      • recurse

        public String recurse​(String vtl)
               throws Exception

        Recursively evaluates a String containing VTL using the current context, and returns the result as a String. It will continue to re-evaluate the output of the last evaluation until an evaluation returns the same code that was fed into it.

        Parameters:
        vtl - the code to be evaluated
        Returns:
        the evaluated code as a String
        Throws:
        Exception
        See Also:
        eval(String)

      • eval

        public String eval​(org.apache.velocity.context.Context ctx,
                   String vtl)
            throws Exception

        Evaluates a String containing VTL using the current context, and returns the result as a String. By default if this fails, then null will be returned, though this tool can be configured to let Exceptions pass through. This evaluation is not recursive.

        Parameters:
        ctx - the current Context
        vtl - the code to be evaluated
        Returns:
        the evaluated code as a String
        Throws:
        Exception

      • recurse

        public String recurse​(org.apache.velocity.context.Context ctx,
                      String vtl)
               throws Exception

        Recursively evaluates a String containing VTL using the current context, and returns the result as a String. It will continue to re-evaluate the output of the last evaluation until an evaluation returns the same code that was fed into it or the number of recursive loops exceeds the set parse depth.

        Parameters:
        ctx - the current Context
        vtl - the code to be evaluated
        Returns:
        the evaluated code as a String
        Throws:
        Exception

      • internalRecurse

        protected String internalRecurse​(org.apache.velocity.context.Context ctx,
                                 String vtl,
                                 int count)
                          throws Exception
        Throws:
        Exception